Recently, a pipe lining technology called pipe renovation has been employed for reestablishing a pipeline by renovation of an obsolete sewage pipeline, for instance.
This pipe renovation is a technology which comprises lining an existing pipeline internally with a continuous strip of synthetic resin wound spirally and filling the gap between the new and old pipelines with a filling agent but when such pipe renovation technology is applied to an existing pipeline having side pipes (branch pipes), it is necessary to drill apertures for the branch lines after application of the filling agent.
Heretofore, where the existing line is made of a magnetic material such as iron, it has been proposed to detect its branch line openings with a magnetic sensor and drill apertures for the branch lines in the detected positions from within the new pipeline. (See, for example, Japanese Patent Publication KOKAI No. 127420/1981)
However, where the existing pipeline is made of a nonmagnetic magnetic material such as concrete, e.g. Hume concrete pipe, the above-mentioned method using a magnetic sensor cannot be employed.
It might be contemplated to insert a drilling machine into the branch line and drill an aperture from the branch line side but in the case of sewage line renovation, it is sometimes difficult to insert a drilling machine into the branch line depending upon the geometry of the pipeline system.